The lead (Pb) and lead dioxide (PbO2) material used for lead-acid battery electrodes (hereinafter the “matrix”) are very porous materials. This porosity allows the electrolyte completely to penetrate the matrix and chemically react within it. This in turn increases the current-carrying capacity of the battery. Without these pores the battery's load carrying ability would suffer greatly. Unfortunately, nothing is gained without giving something up. FIG. 1 illustrates a “like-new, porous electrode” which has not been in contact with electrolyte. FIG. 2 illustrates a similar electrode after six months of use. While lead-acid batteries will be used here for illustrative purposes, analogous considerations apply generally to other chemical-to-electrical energy storage devices employing alternative electrode and electrolytic materials.
When a lead-acid battery discharges, PbSO4's form within the pores and on the surface of the matrix. The formation of PbSO4's on the surface of the matrix does not present a real problem; these sulfates (SO4's) go into solution easily during the charge cycle. It is the formation of PbSO4's within the matrix that deteriorates the battery's capacity over time. After several charge and discharge cycles these PbSO4's build up within the pores. The strength of the bonds created between Pb and SO4 have several different levels. The longer these two molecules remain in contact the stronger the bonds become. If every SO4 is not driven back into solution during the charging process, the remaining PbSO4 bonds grow stronger and stronger, dropping to lower and lower covalent energy levels. At this point the amount of time and current required to break these bonds will have to be increased, and the collateral damage to the battery resulting from such removal increases significantly.
Eventually these stubborn PbSO4 formations will crystallize (sulfation) and block passage of the electrolyte through the matrix. Sulfation lowers the current-carrying capacity and over time limits the energy storage capacity of the battery. It also diminishes the life of the battery and can cause structural damage. It is this limitation that requires users to apply voltages much higher than that of the battery itself in order to recharge it, and that results in batteries being made larger then they would otherwise need to be to store and deliver a given quantity of energy.
The sulfate ion has several different energy-bonding states or energy levels. Over time, there is a transition—a drop in energy level—from a less-stable ionic bond to a very-stable covalent bond. These molecules stack up like shingles to cover the surface of and the porous regions throughout the matrix. The effect is like painting the battery plate with a resistive coating. The useful life of a lead-acid battery is dictated by the ability to break up these deposits.
Early attempts to eliminate lead-acid sulfation began with equalization or “over charging.” This process was successful at removing most of the deposits, but at a very high cost to the battery life span, due to the erosion of the positive plate grid structure. The process, being highly exothermic, results in heat generation, plate warpage and mechanical stress on cell components. There are numerous examples of battery cells exploding as a result of equalization. Later a safer electronic charging process was developed. This improved technique is still unable to remove the oldest and most stable sulfate deposits from the plates. This process still relies on large voltages, and therefore currents, when the charge is applied. Thus, this process also results in the adverse factors mentioned above, and wastes energy. In addition, this process of charging is very time-consuming.
Some efforts to address sulfation focus on improved chemical constituents, for example, U.S. Pat. No. 5,945,236 for an electrolyte additive and U.S. Pat. No. 6,458,489 which alters the concentration of H2SO4 in a lead acid battery.
Many attempts have been made to use large pulsating currents to reduce sulfation and similar deposits. For example:
U.S. Pat. No. 5,491,399 discloses “a fast rise time current pulse for application to a battery” (abstract), which, based on FIGS. 2 and 3, appears to be on the order of a few μsec, which translates to a 500 KHz frequency. This—like virtually all the prior art—is used for “removing the lead sulfate deposits from the battery plates” (column 1, lines 37-38).
U.S. Pat. No. 5,525,892 discloses using “a positive voltage pulse train (characterized by a fast rise time spike followed by a non-uniform hump-shaped trail-off) that is combined with a DC charging current output by the charger” (abstract). “[T]he shape of the trail-off of each pulse is not uniform from pulse to pulse in the pulse train. This fluctuation in the shape characteristics of the pulses within the pulse train is believed to result in improved sulfate deposit removal” (column 1, lines 47-48). “The rise time 208 for the spike portions 204 of the pulses 202 generated by the pulsed battery rejuvenator 10 is approximately four to eight microseconds per pulse” (column 3, lines 55-58), translating to a frequency from about 125 to 250 KHz.
U.S. Pat. No. 5,677,612 discloses that a “battery desulfator operates by taking a small amount of energy from the battery 124, which passes through the oscillator or multivibrator 125, which in turn transforms the battery DC voltage into high frequency pulses which are fed back into the battery 124” (column 2, lines 17-21). While no frequencies are specifically disclosed, it is noted that the “process continues at a rate of several thousand times per second” (column 3, lines 25-26).
U.S. Pat. No. 5,808,447 discloses “pulse charging [which] charges a rechargeable battery by repeatedly alternating periods of charging and suspension of charging” (column 2, lines 30-32). The “400 msec” interval mentioned in column 6, line 6 and elsewhere is suggestive of an approximate 2.5 KHz frequency.
U.S. Pat. No. 6,130,522 discloses “connecting a current source device across the positive and negative terminals of the battery and applying a periodic pulse to the device so as to apply a pulsed current across the battery terminals without applying a voltage pulse” (abstract). “The pulse frequency is selectable over a wide range but preferably is greater than the frequency of the base charger current so that it preferably ranges from 60 Hz to 100,000 Hz” (column 4, lines 55-58).
U.S. Pat. No. 5,891,590 discloses “[a] device and method for reducing crystal formations, which have a range of resonant frequencies, on electrode plates of an electrical battery . . . [using] a train of direct current pulses at a frequency within the range of resonant frequencies . . . ” (abstract). It appears that the “resonant frequencies” referred to something other than chemical bonding resonances, because “[t]he frequency is selected to fall within a range of frequencies that is believed to correspond to the range of resonant frequencies of the lead sulfate crystals. Preferably, the range is in the order of about 10 KHz to 32 KHz and more preferably in a range of about 20 KHz to 32 KHz” (column 4, lines 5-9). The resonant frequency of chemical bonds connecting Pb to SO4 in PbSO4 is in fact on the order of 3.26 MHz at the lowest covalent bonding energy—over 100 times as high as the frequencies discussed here—so it is clear that these chemical bonds are not at all under consideration in U.S. Pat. No. 5,891,590.
Among many other problems, all of U.S. Pat. Nos. 5,491,399; 5,525,892; 5,677,612; 5,808,447; 6,130,522; and 5,891,590 employ frequencies in the sub-500 KHz range, and such low frequencies are insufficient to get at the root cause of lead-acid battery sulfation—namely—the covalent chemical bonds which form between Pb to SO4 in PbSO4, or to address similar plating phenomena in other types of batteries.
U.S. Pat. No. 5,276,393 discloses “[a] solar powered battery reclaiming and charging circuit . . . having a high frequency section . . . and output coupled by a close coupled RF transformer to the battery connected output section. The transformer has a secondary winding producing a current-voltage full wave output sharply defined through a two diode rectifying circuit to a multi-frequency 10 KHz to 100 KHz pulse output. The sharp pulse outputs with RF content in the 2-10 megahertz frequency range have specific frequencies equal to natural resonant frequencies of the specific electrolytes used in respective batteries. These resulting high frequency RF output signals in each pulse envelope structure are capable of reclaiming, maintaining and charging batteries that possess a liquid electrolyte or jell electrolyte and are beneficial to dry cell batteries as well in extending battery life” (abstract, see also column 1, lines 48-68). This patent thus focuses on the resonant frequencies of the “specific electrolytes” under consideration.
U.S. Pat. No. 6,184,650 observes that “[i]t is possible to reverse [i.e., remove, not prevent] the build-up of sulfur crystals on the collectors (plates) of a lead-acid type storage battery. By ‘hitting’ these plates with electrical pulses which produce energy at 3.26 MHz, which is the resonant frequency of a sulfur crystal, the bond is broken, allowing the molecules to dissolve back into the electrolyte solution from which they first came” (column 1, lines 8-15). It is further stated that “[t]his invention is capable of reversing the build-up of crystallized sulfur on the ‘plates’ of a lead-acid storage battery, thereby improving the charge/discharge characteristics of a battery in which such formations have occurred. It accomplishes this process by rapidly turning the charger on and off (rise time=200-500 nsec.) and by generating pulses (1 Amp amplitude) during the ‘float’ charge cycle” (column 1, lines 25-32).
These two patents, U.S. Pat. Nos. 5,276,393 and 6,184,650, provide a more satisfactory frequency range for addressing sulfation. However, they still rely on pulsed electrical stimulation of the battery, which itself wastes energy and damages the battery. This process of periodically sending large voltage spikes into the battery may have desirable short-term effects, but the long-term effects are detrimental to the battery performance and should be avoided. A sharp electrical pulse at such high frequency to remove sulfate deposits which have already formed is akin to attacking the matrix with a jackhammer: the deposits may be removed, but the matrix itself is also damaged in the process.
Although an electrical pulse may contain frequency components required to resonate the crystal's structure, these pulses also contain other frequency components which serve no useful purpose in the minimization of sulfation and therefore improved battery performance. These extra frequency components contain energy and this energy is being wasted unnecessarily. The process of injecting pulsed electrical energy into a covalent bond to create a mechanical response is highly inefficient. This electromagnetic-to-mechanical conversion process is similar to that of a microwave oven. The radiation in a microwave oven is used to mechanically excite the water molecule bonds present in the material. It is well known that the energy required to heat a glass of water from room temperature to the boiling point is much greater than the energy the glass of water actually received. This excess energy is wasted and if there were a more efficient way to inject the energy into the mechanical type bonds of water the microwave would be much more efficient device.
These patents which rely on electrical stimulation are not concerned with this wasted energy. In addition, the large voltages contained within the pulse are applied across water molecules and through electrolysis, so more gassing is likely. This is also a form of wasted energy. Although some gassing is essential to battery performance, too much gassing is detrimental to battery life. Therefore, in achieving its objective, all of these patents which employ electrical stimulation to remove sulfates after they are already formed not only waste valuable energy but also degrade the life of the storage device. If a method could be found that eliminates the need for these high voltages and currents, the wasted energy and the degradation of a storage device could be eliminated. In other words, the performance characteristics of an energy storage device can be improved. Since these patents are not concerned with the amount of energy used to achieve its goal, they shift their focus from energy storage to sulfate minimization and have effectively defeated the underlying foundation of a battery—efficient energy storage.
U.S. Pat. No. 5,872,443 discloses “[a]n electronic method . . . whereby the applied electromotive force optimizes the electrokinetic behavior of charged particles to match closely the natural electrical response and physical structure of the system. The method shapes the electromotive force's amplitude and frequency to normalize the relative interactions between the charged particles and the physical structure.” While interesting as general background, the application of an electromotive force in this patent still poses the same problems as in the aforementioned patents.
A fair number of other patents take a mechanical, rather than electrical approach. For example:
U.S. Pat. Nos. 6,299,998 and 6,458,480 disclose batteries with movable anodes, and U.S. Pat. No. 4,587,182 discloses the use of a “compressive load on the anode which inhibits the formation of a porous deposit of exterior, irregularly oriented, amalgamated lithium grains on the anode” (abstract).
U.S. Pat. No. 3,923,550 discloses that “to avoid dendrite formation when charging an alkaline accumulator battery cell having a zinc anode . . . either the separator or the anode is subjected to a vibratory movement during the charging process” (abstract). “The vibratory movement is suitable carried out with a frequency of 0.01-1000 Hz, preferably 1-500 Hz” (column 2, lines 19-20).
U.S. Pat. No. 5,352,544 discloses “a method for increasing the ionic conductivity of solid polymer electrolytes which comprises mechanically exciting the units which comprise the polymer electrolytes [and] a . . . solid state battery having a solid polymer electrolyte and means for mechanically exciting the polymer electrolyte” (column 2, lines 14-22). In particular, this patent employs “mechanical excitation over a frequency range of 40-400 KHz” (column 3, lines 27-28 and elsewhere).
U.S. Pat. No. 5,932,991 discloses “enhancing the charging of a battery by exposing the battery to acoustic excitation while the battery is being charged” (abstract) and specifically the use of a 20 KHz. frequency (column 3, line 52, and several other places).
U.S. Pat. No. 6,060,198 employs a transducer. “The ultrasonic frequency to be selected and its intensity are functions of the structural characteristics of the entire battery. Usually the frequency range will be between about 20 KHz and about 120 KHz. The required wattage is surprisingly low. Typically between about 10 to about 20 watts output of vibrational energy will be sufficient.” (column 5, lines 31-36). This is a good example of mechanically-based approaches where the frequency and/or pulse rise time is determined by reference to the physical, structural elements of the battery.
U.S. Pat. No. 5,963,008, in a similar vein, discloses that “[e]lectroacoustic battery sonication rehabilitates a battery by decreasing metallic shorting across battery elements through sonication. Sonication may be produced by application of an electrical signal [damaging to the battery as earlier discussed] of selected frequency to the terminals of a battery, thereby establishing a resonant condition within the battery. Alternately, sonication may be provided by transducers placed within a battery and receiving a drive signal of selected frequency to establish a resonant condition within the battery” (abstract). More specifically, it is disclosed that “an appropriate resonant frequency for sonication in a lead acid battery may be approximated under these calculations and, in general, a 200-300 kilohertz frequency is productive. A lower frequency may work to some degree, but will be of lesser effect. Higher frequencies, however, produce vibration of smaller portions of a given body. The nature and shape of the battery elements to be vibrated drives frequency selection to the range suggested herein. A typical lead acid battery grid consists of squares, or a similar shape, of approximately 0.01 m. This characteristic of typical lead acid batteries provided a basis for selecting a 0.01 m wavelength in the above calculations. Other battery configurations would likely exhibit different resonant characteristics and would possibly require different sonication signal frequencies” (column 4, lines 37-51).
The “above calculations” for selecting the “sonication” frequency are set forth in the formulae in column 4, lines 25-34. The frequencies are selected based on the speed of sound in the electrode grid and the size of the typical grid elements, i.e., squares, according to FREQUENCY=VELOCITY OF SOUND IN THE GRID/SIZE OF GRID ELEMENT. According to this approach, using the unbounded lead calculation, one would not employ a frequency as high as 1 MHz unless and until the grid element size reached approximately 2.5 mm, which is very small.
U.S. Pat. No. 5,614,332 is very similar to U.S. Pat. No. 5,963,008 (and U.S. Pat. No. 6,060,198) in its underlying theory of how to select an appropriate frequency for mechanical stimulation. It too discloses a battery in which “electrodes are connected to a charging or discharging circuit and at least one electrode is mechanically manipulated during the charging or discharging” (abstract). “The preferred frequency is on the order of 50 KHz for a battery electrode of characteristic length 10 cm . . . . The frequency scales inversely with the battery electrode size. Thus, a 100 cm long battery electrode would require a 5 KHz minimum frequency” (column 6, lines 9-12). Although “FIG. 13 shows an ultrasonic transducer 132 . . . which can operate at frequencies as high as 2 MHz,” which is still substantially less than, say, the 3.26 MHz frequency of PbSO4, it is clear that such a high frequency—based on the inverse frequency scaling disclosure of this patent later given more precise definition in U.S. Pat. No. 5,963,008—would be employed for a (50 KHz/2000 KHz)×10 cm=2.5 mm long battery electrode, that is, for a micro-battery cell.
This is the same sort of result reached in U.S. Pat. No. 5,963,008, namely, that high frequencies in the MHz. range would be employed only if one was considering very small electrodes or electrode elements, i.e., squares, in the range of millimeters and smaller. As such, while the availability of frequencies “as high as 2 MHz” are noted in passing, U.S. Pat. No. 5,614,332 focuses on ways to “plastically deform” the electrode (see independent claims), and—in the same manner as U.S. Pat. No. 5,963,008—teaches away from the use of higher frequencies unless one is dealing with very small (millimeter-sized) electrodes or electrode squares.
Mechanical stimulation is much preferred to electrical stimulation, because it avoids many of the problems mentioned above with respect to wasted energy and added degradation. However, all of the prior art that involves mechanical stimulation focuses on the physical structures of the battery, and not on the chemistry which bonds the chemical reaction products to the electrodes. They all teach that where mechanical stimulation is concerned, the pertinent data for selecting frequencies are such things as the speed of sound in the medium being vibrated, and the physical size of the battery structure that one is looking to stimulate. Thus, as taught in column 6, lines 9-10 of U.S. Pat. No. 5,614,332, “[t]he frequency scales inversely with the battery electrode size.” And, as taught starting at column 5, line 31 of U.S. Pat. No. 6,060,198, “[t]he ultrasonic frequency to be selected and its intensity are functions of the structural characteristics of the entire battery.” And, as clearly taught in U.S. Pat. No. 5,963,008 at column 4, lines 42-44, “[t]he nature and shape of the of the battery elements to be vibrated drives frequency selection.”
There is no suggestion whatsoever about introducing mechanical excitations at energy levels at which covalent bonds are formed with the electrodes, and indeed, all of the patents which employ sound waves (mechanical stimulation) teach directly away from this by suggesting that frequency is determined based on the physical structure of the battery, and that higher frequencies are of interest only when small structural features are being considered. That is, these patents are wholly focused on manipulating the electrode or the battery structure—to remove not prevent sulfation and like effects in the first place—and not on preventing undesired bonding of chemical reaction products with the electrode.